1. Field of the Invention
The present invention relates to impression material, and the use thereof.
2. Description of the Prior Art
Impression materials having good rubber elasticity and high ultimate tensile strengths, which are obtained from the use of cross-linkable starting compounds, and which polymerize rapidly and completely at room temperature, are known from U.S. Pat. No. 3,453,242. These materials are based on polyethers with aziridine terminal groups, have a minimum molecular weight of 1000 and contain on the average more than one ethylenimine residue per molecule. They have been used for a long period of time with great success, in particular in the field of dentistry, for preparing molds of the jaw in the preparation of prostheses and similar tooth replacements.
The aforementioned aziridine polyethers are worked into a paste with plasticizers, fillers, pigments and taste improvers, which are then mixed with the polymerization initiators described in the above cited patent, whereupon the mixture is applied to the surface to be reproduced. Following cross-linking, the hardened elastic mass may be removed, whereby very accurate moldings are obtained.
A disadvantage of these impression materials consists of the fact that they have a certain adhesive effect, and that consequently the polymerized material is occasionally difficult to remove from the object to be produced. Especially when used as a dental impression material, it may occur on occasion that the imprint is somewhat difficult to remove from the mouth, as the impression material exhibits a certain adhesion to natural teeth, synthetic plastic teeth and also metal crowns. It may even occur in individual cases that particularly exposed parts, such as for example extensions into interdental spaces, are torn off during the removal of the impression.
In order to prevent adhesive effects, it is known to add silicones, waxes, metal soaps, certain polymers or talcum and mica as separating materials to the different molding materials. However, these additions are entirely without effect on the abovementioned materials based on aziridino compounds, or they alter the properties of the impression material detrimentally to such an extent that it becomes useless. Thus, the impression material may be rendered hydrophobic so strongly that particularly when used as a dental impression material, it no longer flows adequately onto the wet parts of the mouth, thereby impairing the molding accuracy, or the swelling or shrinking behavior of the elastic moldings are affected negatively to the extent that the dimensional stability of the impression obtained is no longer assured over a longer period of time.